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Journal of Virology, January 2005, p. 1207-1214, Vol. 79, No. 2
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.2.1207-1214.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

A Surface Loop of the Potato Leafroll Virus Coat Protein Is Involved in Virion Assembly, Systemic Movement, and Aphid Transmission

Lawrence Lee,^1, Igor B. Kaplan,² Daniel R. Ripoll,³ Delin Liang,^2, Peter Palukaitis,⁴ and Stewart M. Gray^1,2*

Plant Soil & Nutrition Laboratory, USDA Agricultural Research Service,¹ Department of Plant Pathology,² Computational Biology Service Unit, Cornell Theory Center, Cornell University, Ithaca, New York,³ Scottish Crop Research Institute, Invergowrie, Dundee, United Kingdom⁴

Received 18 June 2004/ Accepted 31 August 2004

Two acidic domains of the Potato leafroll virus (PLRV) coat protein, separated by 55 amino acids and predicted to be adjacent surface features on the virion, were the focus of a mutational analysis. Eleven site-directed mutants were generated from a cloned infectious cDNA of PLRV and delivered to plants by Agrobacterium-mediated mechanical inoculation. Alanine substitutions of any of the three amino acids of the sequence EWH (amino acids 170 to 172) or of D177 disrupted the ability of the coat protein to assemble stable particles and the ability of the viral RNA to move systemically in four host plant species. Alanine substitution of E109, D173, or E176 reduced the accumulation of virus in agrobacterium-infiltrated tissues, the efficiency of systemic infection, and the efficiency of aphid transmission relative to wild-type virus, but the mutations did not affect virion stability. A structural model of the PLRV capsid predicted that the amino acids critical for virion assembly were located within a depression at the center of a coat protein trimer. The other amino acids that affected plant infection and/or aphid transmission were predicted to be located around the perimeter of the depression. PLRV virions play key roles in phloem-limited virus movement in plant hosts as well as in transport and persistence in the aphid vectors. These results identified amino acid residues in a surface-oriented loop of the coat protein that are critical for virus assembly and stability, systemic infection of plants, and movement of virus through aphid vectors.

Present address: U.S. Horticultural Research Laboratory, USDA ARS, Fort Pierce, Fla.

Present address: Department of Molecular Microbiology & Immunology, University of Southern California, Los Angeles, Calif.

This article has been cited by other articles:

• Peter, K. A., Liang, D., Palukaitis, P., Gray, S. M. (2008). Small deletions in the potato leafroll virus readthrough protein affect particle morphology, aphid transmission, virus movement and accumulation. J. Gen. Virol. 89: 2037-2045 [Abstract] [Full Text]  
• Kaplan, I. B., Lee, L., Ripoll, D. R., Palukaitis, P., Gildow, F., Gray, S. M. (2007). Point mutations in the potato leafroll virus major capsid protein alter virion stability and aphid transmission. J. Gen. Virol. 88: 1821-1830 [Abstract] [Full Text]